1. Field of the Invention
The present invention generally relates to methods of manufacturing field emitters, and more particularly to a method of fabricating a sub-100 nanometer field emitter tip out of group III-nitride semiconductors for use in vacuum microelectronic devices.
2. Description of the Related Art
The quantum-mechanical phenomenon known as field emission, otherwise referred to as cold emission, occurs when electrons tunnel through an energy barrier at an emitter surface/vacuum interface and through a vacuum subjected to an applied electric field. Typically, the emitter surface is a metal or semiconductor material. This field emission of electrons provides a cold cathode for use in flat panel displays and other vacuum microelectronic devices and applications.
The electron affinity of a particular material (emitter surface material) affects the level of the barrier that the electrons must overcome. While most materials have a large positive electron affinity, some materials have a low or even negative electron affinity. For example, group III-nitride semiconductor materials possess very low electron affinity.
A field emitter's geometry greatly affects its emission characteristics; that is the emission of electrons from one solid material to another. In practice, it has been discovered that field emission is most easily obtained from pointed shapes, such as pointed needles or tips having smoothed hemispherically-contoured ends. The cone shape cathode leads to an increased electric field strength above the cathode relative to the electric field strength at the cathode's surface. With an applied bias, the potential barrier is then sufficiently reduced for electrons to tunnel through leading to a current. These cone shaped tips are referred to as Spindt cathodes.
Field emitter tips are usually fabricated in one of two ways. In a first conventional approach, sequential anisotropic or isotropic etching techniques are used to form sharp tip ends for field emitters. In a second conventional approach, material growth or deposition techniques are used to form structures with submicron scale emission tips. However, the conventional approaches have yet to provide an etch technique for producing field emitter tips from group III-nitride semiconductor materials. Moreover, other shortcomings of the conventional approaches are that the growth techniques are not well developed and have not shown to produce successful Spindt-type group III-nitride field emitter tips with a tip radius near 100 nm.
For high-power and high-frequency applications such as radar, electronic warfare, and space-based communications, vacuum tubes were the conventional preferred devices. However, as the need for even smaller devices becomes prevalent to satisfy the needs of energy efficiency, greater system reliability, and cost efficiency, such vacuum tubes are no longer preferable due to their excessive size, cost, fabrication complexities, and general inapplicability in other applications.
Therefore, there remains a need for an improved process of fabricating a sub-100 nanometer field emitter tip out of group III-nitride semiconductors for use in vacuum microelectronic devices, which overcome the deficiencies of the conventional approaches and result in higher quality field emitter tips.